US20120091845A1 - Brushless motor - Google Patents
Brushless motor Download PDFInfo
- Publication number
- US20120091845A1 US20120091845A1 US13/274,082 US201113274082A US2012091845A1 US 20120091845 A1 US20120091845 A1 US 20120091845A1 US 201113274082 A US201113274082 A US 201113274082A US 2012091845 A1 US2012091845 A1 US 2012091845A1
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- Prior art keywords
- magnet
- rotor
- core
- poles
- circumferential
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K1/00—Details of the magnetic circuit
- H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
- H02K1/22—Rotating parts of the magnetic circuit
- H02K1/27—Rotor cores with permanent magnets
- H02K1/2706—Inner rotors
- H02K1/272—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis
- H02K1/274—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets
- H02K1/2746—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets the rotor consisting of magnets arranged with the same polarity, e.g. consequent pole type
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K1/00—Details of the magnetic circuit
- H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
- H02K1/22—Rotating parts of the magnetic circuit
- H02K1/27—Rotor cores with permanent magnets
- H02K1/2706—Inner rotors
- H02K1/272—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis
- H02K1/274—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets
- H02K1/2753—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets the rotor consisting of magnets or groups of magnets arranged with alternating polarity
- H02K1/276—Magnets embedded in the magnetic core, e.g. interior permanent magnets [IPM]
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K2201/00—Specific aspects not provided for in the other groups of this subclass relating to the magnetic circuits
- H02K2201/03—Machines characterised by aspects of the air-gap between rotor and stator
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K2213/00—Specific aspects, not otherwise provided for and not covered by codes H02K2201/00 - H02K2211/00
- H02K2213/03—Machines characterised by numerical values, ranges, mathematical expressions or similar information
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K29/00—Motors or generators having non-mechanical commutating devices, e.g. discharge tubes or semiconductor devices
- H02K29/03—Motors or generators having non-mechanical commutating devices, e.g. discharge tubes or semiconductor devices with a magnetic circuit specially adapted for avoiding torque ripples or self-starting problems
Definitions
- the present invention relates to a brushless motor including a rotor with a consequent-pole structure.
- a brushless motor includes a rotor and a stator (refer to, for example, Japanese Laid-Open Patent Publication No. 2004-201406).
- the rotor includes a rotor core.
- the rotor core includes a plurality of magnet poles (referred hereafter as the magnet poles) and a plurality of core magnet poles (hereafter referred to as the core poles).
- the magnet poles are arranged in the circumferential direction of the rotor core.
- Each of the core poles is arranged between two magnet poles that are adjacent to each other in the circumferential direction.
- a magnet is embedded in each magnet pole.
- a void is formed at a boundary between the core pole and the magnet pole that are adjacent to each other in the circumferential direction.
- the stator includes a plurality of teeth arranged at equal angular intervals in the circumferential direction.
- the teeth face the rotor in the radial direction.
- Coils are set on the teeth of the stator.
- the number of magnets used in the rotor is decreased by one half without significantly lowering performance.
- the brushless motor is advantageous in that it requires fewer resources and reduces costs.
- the adjacent tooth when there is more than one tooth facing a single magnet, that is, when the adjacent tooth also faces the same magnet pole in the radial direction, the adjacent tooth may demagnetize the magnet pole. This may cause a torque decrease that lowers the rotation performance of the rotor.
- one aspect of the present invention provides a brushless motor provided with a rotor including a rotor core.
- the rotor core includes a plurality of magnet poles, which are arranged in a circumferential direction of the rotor core, and a plurality of core poles, each arranged between two adjacent ones of the magnet poles in the circumferential direction.
- a magnet is embedded in each of the magnet poles.
- a void is formed at a boundary between each of the core poles and an adjacent one of the magnet poles in the circumferential direction.
- a stator includes a plurality of teeth, which are arranged at equal angular intervals in the circumferential direction facing the rotor in a radial direction of the rotor, and a plurality of coils, each wound around the teeth.
- Each magnet pole includes a peripheral core portion located closer to the stator than the corresponding magnet in the radial direction of the rotor.
- At least one of the two voids formed at opposite circumferential sides of each magnet pole includes an extended void region that extends into the corresponding peripheral core portion and toward a middle point of the magnet pole in the circumferential direction.
- FIG. 1 is a schematic diagram showing the structure of a brushless motor according to one embodiment of the present invention
- FIG. 2 is a plan view showing part of the rotor shown in FIG. 1 ;
- FIG. 3 is a perspective view showing a magnet pole shown in FIG. 1 ;
- FIG. 4 is a graph showing characteristic curves indicating the relationship between the tilt angle of magnets and the change rate of magnetic flux
- FIG. 5 is a plan view showing part of a rotor in a further embodiment
- FIG. 6 is a perspective view showing a magnet pole of the rotor in another embodiment
- FIG. 7 is a plan view showing part of a rotor in a further embodiment of the present invention.
- FIG. 8 is a graph showing the characteristic curves indicating the relationship between the ratio W 2 /W 1 (the ratio of the magnet width W 2 to the circumferential width W 1 of the first opposing surface) and the change rate of magnetic flux;
- FIG. 9 is a schematic diagram showing part of a brushless motor structure in which the edge depth E is set at 0;
- FIG. 10 is a schematic diagram showing part of a brushless motor structure in which the edge depth E is set at 0;
- FIG. 11 is a plan view showing part of a rotor in a further embodiment of the present invention.
- FIG. 12 is a plan view showing part of a rotor in a further embodiment of the present invention.
- an inner rotor type brushless motor 1 of the present embodiment includes an annular stator 2 and a rotor 3 arranged inward in the radial direction from the stator 2 .
- the stator 2 includes a stator core 4 .
- the stator core 4 includes an annular part 11 and a plurality of (twelve in the present embodiment) teeth 12 .
- the teeth 12 are arranged in the circumferential direction and extend inward in the radial direction from the annular part 11 .
- the stator core 4 is formed by a stacking a plurality of core sheets in the axial direction. Each core sheet is formed by a metallic sheet having high permeability.
- a coil 13 is wound around each tooth 12 of the stator core 4 with an insulator (not shown) arranged in between. The coils 13 generate magnetic field, which rotates the rotor 3 .
- Each coil 13 is wound around a predetermined one of the teeth 12 and forms one of three-phases, namely, a U-phase, a V-phase, and a W-phase. Each coil 13 is wound in the same direction (counterclockwise when viewed the teeth 12 from the inner circumferential side) into a concentrated winding.
- Each tooth 12 has a curved distal surface 12 a , and the distal surfaces 12 a of the teeth 12 lie along the same circle.
- the rotor 3 includes a rotor core 22 having an annular shape.
- a rotary shaft 21 is fitted into the rotor core 22 .
- the rotor core 22 is formed by stacking core sheets 22 a (refer to FIG. 3 ) in the axial direction.
- Each core sheet 22 a is a metallic sheet having high permeability.
- Four magnets 23 functioning as north poles are embedded in the rotor core 22 near the outer circumferential surface of the rotor core 22 .
- the magnets 23 are arranged at equal angular intervals (intervals of 90 degrees) in the circumferential direction.
- Each magnet 23 is formed by a generally rectangular plate.
- the rotor core 22 also includes two bridges 31 and a peripheral core portion 32 for each magnet 23 .
- the bridges 31 extend in the circumferential direction along opposite side surfaces of the magnet 23 .
- the peripheral core portion 32 is arranged outward in the radial direction from the magnet 23 (toward the stator 2 from the rotor core 22 ) and is supported by the two bridges 31 .
- the peripheral core portion 32 and the magnet 23 form a magnet pole 24 .
- four magnet poles 24 are arranged at equal angular intervals of 90 degrees on the outer circumference of the rotor core 22 .
- Core poles 25 which project from the rotor core 22 , are arranged between adjacent magnet poles 24 with voids S 1 and S 2 formed at boundaries between the magnet poles 24 and the core poles 25 .
- the voids S 1 and S 2 are arranged at two opposite sides of each magnet pole 24 in the circumferential direction.
- the void S 1 is located at the rear side of the magnet pole 24 relative to the rotation direction of the rotor 3 (clockwise in FIGS. 1 and 2 ).
- the void S 2 is located at the front side of the magnet pole 24 relative to the rotation direction of the rotor 3 .
- the magnets 23 and the core poles 25 are arranged alternately at equal angular intervals (intervals of 45 degrees) in the circumferential direction.
- the rotor 3 includes eight magnet poles in total and has a consequent-pole structure in which the magnets 23 function as north poles and the core poles 25 function as south poles.
- Each core pole 25 has a curved surface 25 a (surface facing the stator 2 ), and the curved surfaces 25 a of the core poles 25 lie along the same circle C as viewed from the axial direction.
- the circle C is a hypothetical circle extending along the outer circumference of the rotor 3 .
- Each pair of bridges 31 in the rotor core 22 is in contact with the two circumferential side surfaces of the corresponding magnet 23 and connects the corresponding peripheral core portion 32 to a central portion (main core portion 22 b ) of the rotor core 22 .
- the peripheral core portions 32 and the main core portion 22 b are in contact with the surfaces of the magnets 23 (the two opposite surfaces of the magnets 23 in the radial direction). In this manner, the magnets 23 are in contact with the rotor core 22 on its four sides as viewed in the axial direction. Thus, the magnets 23 are rigidly held in the rotor core 22 .
- each bridge 31 includes a plurality of holes 33 arranged in the axial direction and extending in the circumferential direction.
- each core sheet 22 a of the rotor core 22 includes a recess 22 c , which hollows in the axial direction.
- the holes 33 in the bridge 31 are formed by the recesses 22 c of the core sheets 22 a.
- each peripheral core portion 32 has a surface facing the distal surface 12 a of the teeth 12 .
- the surface facing the distal surface 12 a of the tooth 12 is formed by a first opposing surface 32 a and a second opposing surface 32 b , which are arranged in the circumferential direction.
- the first opposing surface 32 a extends from a first circumferential end of the peripheral core portion 32 (front end in the rotation direction) to a predetermined circumferential intermediate position P.
- the second opposing surface 32 b extends from the circumferential intermediate position P of the peripheral core portion 32 to a second circumferential end (rear end in the rotation direction).
- the surface of the peripheral core portion 32 is formed by the first opposing surface 32 a , which is located at the front side relative to the rotation direction of the rotor 3 , and the second opposing surface 32 b , which is located at the rear side relative to the rotation direction of the rotor 3 .
- the first opposing surfaces 32 a are curved and lie along the same circle C as viewed in the axial direction.
- the first opposing surfaces 32 a of the peripheral core portions 32 lie along the same circle C as the surfaces 25 a of the core poles 25 .
- the first opposing surfaces 32 a are spaced apart from the teeth 12 in the radial direction by a distance that is constant in the circumferential direction.
- Each first opposing surface 32 a has a circumferential width W 1 that is equal to the circumferential width of the distal surface 12 a of each tooth 12 (i.e., the surface facing the rotor 3 in the radial direction).
- the second opposing surfaces 32 b are flat.
- the circumferential width of each second opposing surface 32 b is less than the circumferential width W 1 of each first opposing surface 32 a .
- the second opposing surfaces 32 b are located inward in the radial direction from the circle C along which the first opposing surfaces 32 a lie.
- the distance between each second opposing surface 32 b and the teeth 12 is greater than the distance between each first opposing surface 32 a and the teeth 12 .
- the second opposing surface 32 b is formed so that the distance from the teeth 12 in the radial direction gradually increases in the circumferential direction from the intermediate position P of the corresponding peripheral core portion 32 to the second circumferential end of the peripheral core portion 32 .
- each void S 1 which is located at the rear side of the corresponding magnet pole 24 relative to the rotation direction, extends to a region located outward in the radial direction from the magnet pole 24 (toward the stator 2 ).
- the extended region of the void S 1 (hereafter referred to as the extended void region Sa) extends along the second opposing surface 32 b to the circumferential intermediate position P of the corresponding peripheral core portion 32 .
- the extended void region Sa extends from an outer radial end of the void S 1 to the middle part of the peripheral core portion 32 in the circumferential direction (toward the middle point of the magnet pole). As a result, the extended void region Sa extends to a position located outward in the radial direction (toward the stator 2 ) from the magnet 23 arranged in the magnet pole 24 .
- the void S 2 which is located at the front side in the rotational direction, has an area T 2
- each magnet 23 which has two parallel long sides and two parallel short sides, is arranged so that its long sides, as viewed in the axial direction, are inclined at a magnet inclination angle ⁇ 1 relative to a straight line L 2 that is orthogonal to a straight line L 1 extending in the radial direction of the stator core 4 through the middle point of the first opposing surface 32 a of the peripheral core portion 32 in the circumferential direction.
- the magnet 23 is inclined so that its rear end relative to the rotation direction is closer to the center of the rotor 3 , as viewed in the axial direction.
- the magnet width W 2 which is the distance between the two ends of the magnet 23 in the circumferential direction, is greater than the width W 1 of the first opposing surface 32 a in the circumferential direction.
- each second opposing surface 32 b is inclined relative to a direction orthogonal to the long sides, or longitudinal direction, of the magnet 23 (the direction in which the short sides of the magnet 23 extends) at a void inclination angle ⁇ 2 .
- the coils 13 are supplied with a driving power to generate a rotational magnetic field that rotates the rotor 3 in the clockwise direction.
- the magnet poles 24 generate torque that rotates the rotor 3 mainly at the first opposing surfaces 32 a of the peripheral core portions 32 .
- one first opposing surface 32 a faces one tooth 12 (e.g., tooth 12 b in FIG. 1 )
- the adjacent tooth 12 faces the corresponding second opposing surface 32 b .
- the gap between the second opposing surface 32 b and the tooth 12 c is large due to the presence of the extended void region Sa. This reduces demagnetization in the magnet pole 24 caused by the tooth 12 c .
- the magnet 23 is inclined so that the surface of the peripheral core portion 32 becomes farther as the rear end of the magnet 23 in the rotation direction becomes closer. This reduces the influence of the tooth 12 c on the magnet pole 24 .
- FIG. 4 shows the change rate of the magnetic flux produced by the magnet pole 24 when the magnet inclination angle ⁇ 1 is varied in the range of 0 to 30 degrees.
- FIG. 4 shows four cases in which the void inclination angle ⁇ 2 is set at 30, 45, 60, and 75 degrees, respectively.
- the magnet inclination angle ⁇ 1 that is set at 0 degree is used as a reference (in which the magnetic flux change rate is 1).
- the magnetic flux change rate is greater than 1.
- the magnetic flux density increases and is in a satisfactory range when the void inclination angle ⁇ 2 is set to 45 degrees or less and the magnet inclination angle ⁇ 1 is set in the range of 0° ⁇ 2 ⁇ 22.5°.
- the void inclination angle ⁇ 2 and the magnet inclination angle ⁇ 1 are set in the above range to increase the magnetic flux density.
- the void S 1 between each magnet pole 24 and the adjacent core pole 25 includes the extended void region Sa, which extends into the peripheral core portion 32 toward the middle point of the magnet pole 24 in the circumferential direction.
- the extended void region Sa is arranged between the teeth 12 and part of each magnet pole 24 in the circumferential direction.
- the extended void region Sa reduces the influence of the adjacent tooth 12 on the magnet pole 24 . This reduces demagnetization in the magnet pole 24 caused by the adjacent tooth 12 . As a result, the torque is increased, and the rotation performance is improved.
- each peripheral core portion 32 includes the first opposing surface 32 a , which faces the teeth 12 and is spaced apart from the opposing tooth 12 by a first distance, and the second opposing surface 32 b , which faces the teeth 12 and is spaced apart through the extended void region Sa from the corresponding teeth 12 by a second distance that is larger than the first distance.
- the width W 1 of the first opposing surface 32 a in the circumferential direction is equal to the width of the distal surface 12 a of each tooth 12 in the circumferential direction. This efficiently generates torque with the first opposing surfaces 32 a . As a result, even though the second opposing surfaces 32 a reduce demagnetization, the decrease in torque is minimized.
- each magnet 23 is formed by a rectangular plate.
- the magnet 23 is arranged so that its long sides, as viewed in the axial direction of the rotor 3 , are inclined at the magnet inclination angle ⁇ 1 relative to the straight line L 2 that is orthogonal to the straight line L 1 extending in the radial direction of the stator core 4 through the middle point of the first opposing surface 32 a in the circumferential direction.
- the second opposing surface 32 b is flat and inclined at the void inclination angle ⁇ 2 relative to the direction in which the short sides of the corresponding magnet 23 extend.
- the magnet inclination angle ⁇ 1 is set in the range of 0° ⁇ 1 ⁇ 22.5°.
- the void inclination angle ⁇ 2 is set in the range of ⁇ 2 ⁇ 45°. This increases the magnetic flux density (refer to FIG. 4 ) ensures further improvement in the rotation performance of the rotor 3 .
- each bridge 31 includes the holes 33 arranged in the axial direction.
- the holes 33 reduce passage of magnetic flux through the bridge 31 and prevent leakage of the magnetic field from the bridge 31 .
- the rotor core 22 the core sheets 22 a that are stacked in the axial direction.
- the recesses 22 c in the core sheets 22 a form the holes 33 of each bridge 31 .
- the holes 33 are easily formed in each bridge 31 of the rotor core 22 by forming the recess 22 c in each core sheet 22 a and then stacking the core sheets 22 a.
- the rotor 3 is rotatable in only one direction (clockwise direction as viewed in FIG. 1 ).
- Each magnet 23 is inclined so that portions closer to the front relative to the rotation direction are closer to the surface of the rotor 3 (i.e., the surface of the corresponding peripheral core portion 32 ). This increases the rotation torque.
- the rotor 3 rotates in the clockwise direction.
- the rotation direction of the rotor 3 may be changed to the counterclockwise direction without changing the structure of the rotor 3 .
- the bridges 31 are arranged on the two opposite ends of each magnet 23 in the circumferential direction.
- the voids S 1 and S 2 formed between the magnet poles 24 and the core poles 25 function as grooves that open outward in the radial direction.
- the bridges 31 may be modified to, for example, bridges 42 shown in FIGS. 5 and 6 .
- the bridges 42 extend in the circumferential direction of the rotor core 22 to connect the peripheral core portions 41 and the core poles 25 .
- the bridges 42 extend in the circumferential direction from two opposite ends of each peripheral core portion 41 and are connected to the surfaces 25 a of the adjacent core poles 25 . In the structure shown in FIGS.
- the surface of the rotor 3 is formed by the outer circumferential surfaces of the bridges 42 in addition to the surfaces 41 a and 25 a of the peripheral core portion 41 and the core pole 25 .
- the width W 1 of the surface 41 a of each peripheral core portion 41 (i.e., the surface facing the teeth 12 ) in the circumferential direction is equal to the width of the distal surface 12 a of each tooth 12 in the circumferential direction.
- the rotor core 22 includes engagement projections 43 , which prevent displacement of the magnets 23 .
- the bridges 42 are not in contact with the two opposite ends of the corresponding magnets 23 in the circumferential direction. In this case, the magnets 23 are easily embedded in the rotor core 22 . In the structure shown in FIGS.
- the bridges 42 cover the outer side (portion closer to the stator 2 ) of the voids S 1 and S 2 between the magnet poles 24 and the core poles 25 .
- the extended void region Sa of each void S 1 extends into the corresponding peripheral core portion 41 .
- each peripheral core portion 32 includes a single first opposing surface 32 a and a single second opposing surface 32 b .
- each peripheral core portion 32 may include a first opposing surface 32 a located in the middle of the surface of the peripheral core portion 32 in the circumferential direction and two second opposing surfaces 32 b located at the two opposite sides of the first opposing surface 32 a in the circumferential direction.
- the voids S 1 and S 2 at the two circumferential ends of each magnet pole 24 each include an extended void region Sa. This structure may be used when the rotor 3 is rotatable in both forward and rearward directions.
- this structure reduces demagnetization in the magnet pole 24 caused by the adjacent tooth 12 in a preferable manner regardless of whether the rotor 3 rotates in the forward direction or the rearward direction.
- the second opposing surfaces 32 b are curved toward the center of the rotor 3 .
- the second opposing surfaces 32 b are curved away from the stator 2 as viewed in the axial direction.
- the distance between the peripheral core portion 32 and the teeth 12 suddenly changes at the two circumferential ends of the peripheral core portion 32 . This reduces demagnetization at the second opposing surfaces 32 b in a preferable manner.
- the magnets 23 are arranged so that its longitudinal direction, as viewed in the axial direction, is orthogonal to a straight line L 1 that extends in the radial direction of the rotor core 22 through the circumferential middle point of the magnet pole 24 .
- Each magnet pole 24 is symmetric relative to the straight line L 1 .
- FIG. 8 shows the change rate of the magnetic flux at the magnet poles 24 in the structure shown in FIG. 7 when the ratio W 2 /W 1 is varied.
- the ratio W 2 /W 1 is the ratio of the width W 2 of the magnet 23 and the width W 1 of the first opposing surface 32 a in the circumferential direction.
- FIG. 8 shows five cases in which the ratio E/A is set at 0, 1, 2, 4, and 6, respectively.
- the ratio E/A is the ratio of the distance E from the two ends of the peripheral core portion 32 in the direction parallel to the short sides of the magnet 23 (the vertical direction in FIG. 7 ) to the circle C (edge depth E in FIG.
- FIG. 9 is a referential diagram showing a structure in which the edge depth E is 0 is substantially equal to the magnet width W 2 and the circumferential width W 1 of the first opposing surface 32 a (i.e., structure of ratio W 2 /W 1 ⁇ 1).
- FIG. 10 is a graph showing the characteristics when the width W 1 of the first opposing surface 32 a in the circumferential direction is set equal to the distal surface 12 a of the tooth 12 and the volume of the magnet 23 is constant as shown in FIGS. 9 and 10 and the magnet width W 2 is varied.
- the edge depth ratio E/A that is set at 0 is used as a reference (in which the magnetic flux change ratio is 1).
- the edge depth ratio E/A is set at 0 and the ratio W 2 /W 1 in the range of 1.0 ⁇ W 2 /W 1 ⁇ 2.1, the magnetic flux density increased and is thus in a satisfactory range.
- the structure in which the edge depth ratio E/A is set at 0 and the ratio W 2 /W 1 is set in the range of 1.0 ⁇ W 2 /W 1 ⁇ 2.1 reduces demagnetization, and increases the torque, and improves the rotation performance.
- the edge depth ratio E/A set at 4 or less and the ratio W 2 /W 1 set in the range of 1.2 ⁇ W 2 /W 1 ⁇ 1.8 also increase the magnetic flux density in an optimum manner.
- the structure in which the edge depth ratio E/A is set at 4 or less and the ratio W 2 /W 1 is set in the range of 1.2 ⁇ W 2 /W 1 ⁇ 1.8 reduces demagnetization, increases the torque, and improves the rotation performance.
- the edge depth ratio E/A is 6, the magnetic flux change ratio is 1 or less regardless of the ratio W 2 /W 1 .
- each of the magnet pole 24 and the core pole 25 are arranged to be symmetric relative to a circumferential middle line but not particularly limited to such a structure.
- the magnet pole 24 and core pole 25 may be in an asymmetric arrangement such as that shown in FIG. 11 .
- the circumferentially middle part in the surface of the peripheral core portion 32 defines the first opposing surface 32 a .
- the opposite sides of the first opposing surface 32 a defines the second opposing surfaces 32 b and 32 c , which are inwardly curved.
- the void S 1 includes an extended void region Sa
- the void S 2 includes an extended void region Sb.
- the extended void regions Sa and Sb are formed to have different cross-sectional areas as viewed in the axial direction.
- the magnet 23 of each magnet pole 24 is arranged in the rotor core 22 so that the longitudinal direction of the magnet 23 as viewed in the axial direction of the rotor 3 is inclined by a magnet inclination angle ⁇ 1 relative to a straight line L 2 , which is orthogonal to a straight line L 1 extending in the radial direction of the stator core 4 through the middle point of the first opposing surface 32 a of the peripheral core portion 32 in the circumferential direction.
- the magnet 23 is inclined so that the end located at the rear side relative to the rotational direction as viewed in the axial direction is closer to the center of the rotor 3 .
- At least one of the second opposing surfaces 32 b and 32 c which are inwardly curved, may be squeezed for formation from the peripheral side. This increases the density at the end of the peripheral core portion 32 in the circumferential direction and further improves the demagnetization resistance.
- the surface of the peripheral core portion 41 defining the extended void region Sa is flat but not particularly limited in such a manner.
- the surface of the peripheral core portion 41 defining the extended void region Sa may be a curved surface 41 b , which hollows toward the magnet 24 .
- the curved surface 41 b may be squeezed from the peripheral side for formation. This increases the density at the end of the peripheral core portion 41 that is closer to the void S 1 and further improves the demagnetization resistance.
- the shapes of the magnets 23 and the shape of the rotor core 22 which includes the peripheral core portions 32 , the core poles 25 , and the bridges 31 , may be changed.
- the rotor 3 includes eight magnet poles, namely, the four magnet poles 24 and the four core poles 25 .
- the rotor 3 may include an (n+1) number (whereas n is a natural number) of magnet poles 24 and an (n+1) number of core poles 25 , which total to 2(n+1) number of poles.
- the stator 2 includes twelve teeth 12 and twelve slots.
- the stator 2 may include 3(m+1) number (whereas m is a natural number) of slots.
- the brushless motor 1 in the above embodiment is of an inner rotor type but may be of an outer rotor type.
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- Engineering & Computer Science (AREA)
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- Permanent Field Magnets Of Synchronous Machinery (AREA)
- Iron Core Of Rotating Electric Machines (AREA)
- Brushless Motors (AREA)
- Permanent Magnet Type Synchronous Machine (AREA)
Abstract
A brushless motor includes a rotor and a stator. The rotor is provided with a rotor core including a plurality of magnet poles and a plurality of core poles. A void is formed at a boundary between each core pole and an adjacent magnet pole in the circumferential direction. Each magnet pole includes a peripheral core portion located closer to the stator than the magnet in the radial direction of the rotor. The void formed in at least one of two circumferential sides of each magnet pole includes an extended void region that extends into the peripheral core portion toward a middle point of the magnet pole in the circumferential direction.
Description
- The present invention relates to a brushless motor including a rotor with a consequent-pole structure.
- A brushless motor includes a rotor and a stator (refer to, for example, Japanese Laid-Open Patent Publication No. 2004-201406). The rotor includes a rotor core. The rotor core includes a plurality of magnet poles (referred hereafter as the magnet poles) and a plurality of core magnet poles (hereafter referred to as the core poles). The magnet poles are arranged in the circumferential direction of the rotor core. Each of the core poles is arranged between two magnet poles that are adjacent to each other in the circumferential direction. A magnet is embedded in each magnet pole. A void is formed at a boundary between the core pole and the magnet pole that are adjacent to each other in the circumferential direction. The stator includes a plurality of teeth arranged at equal angular intervals in the circumferential direction. The teeth face the rotor in the radial direction. Coils are set on the teeth of the stator. In such a brushless motor, the number of magnets used in the rotor is decreased by one half without significantly lowering performance. Thus, the brushless motor is advantageous in that it requires fewer resources and reduces costs.
- In the brushless motor described in the publication, when there is more than one tooth facing a single magnet, that is, when the adjacent tooth also faces the same magnet pole in the radial direction, the adjacent tooth may demagnetize the magnet pole. This may cause a torque decrease that lowers the rotation performance of the rotor.
- It is an object of the present invention to provide a brushless motor including a rotor with a consequent-pole structure that reduces demagnetization, increases the torque, and improves the rotation performance.
- To achieve the above object, one aspect of the present invention provides a brushless motor provided with a rotor including a rotor core. The rotor core includes a plurality of magnet poles, which are arranged in a circumferential direction of the rotor core, and a plurality of core poles, each arranged between two adjacent ones of the magnet poles in the circumferential direction. A magnet is embedded in each of the magnet poles. A void is formed at a boundary between each of the core poles and an adjacent one of the magnet poles in the circumferential direction. A stator includes a plurality of teeth, which are arranged at equal angular intervals in the circumferential direction facing the rotor in a radial direction of the rotor, and a plurality of coils, each wound around the teeth. Each magnet pole includes a peripheral core portion located closer to the stator than the corresponding magnet in the radial direction of the rotor. At least one of the two voids formed at opposite circumferential sides of each magnet pole includes an extended void region that extends into the corresponding peripheral core portion and toward a middle point of the magnet pole in the circumferential direction.
- Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
- The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:
-
FIG. 1 is a schematic diagram showing the structure of a brushless motor according to one embodiment of the present invention; -
FIG. 2 is a plan view showing part of the rotor shown inFIG. 1 ; -
FIG. 3 is a perspective view showing a magnet pole shown inFIG. 1 ; -
FIG. 4 is a graph showing characteristic curves indicating the relationship between the tilt angle of magnets and the change rate of magnetic flux; -
FIG. 5 is a plan view showing part of a rotor in a further embodiment; -
FIG. 6 is a perspective view showing a magnet pole of the rotor in another embodiment; -
FIG. 7 is a plan view showing part of a rotor in a further embodiment of the present invention; -
FIG. 8 is a graph showing the characteristic curves indicating the relationship between the ratio W2/W1 (the ratio of the magnet width W2 to the circumferential width W1 of the first opposing surface) and the change rate of magnetic flux; -
FIG. 9 is a schematic diagram showing part of a brushless motor structure in which the edge depth E is set at 0; -
FIG. 10 is a schematic diagram showing part of a brushless motor structure in which the edge depth E is set at 0; -
FIG. 11 is a plan view showing part of a rotor in a further embodiment of the present invention; and -
FIG. 12 is a plan view showing part of a rotor in a further embodiment of the present invention. - One embodiment of the present invention will now be described with reference to the drawings.
- As shown in
FIG. 1 , an inner rotor typebrushless motor 1 of the present embodiment includes anannular stator 2 and arotor 3 arranged inward in the radial direction from thestator 2. - The
stator 2 includes astator core 4. Thestator core 4 includes anannular part 11 and a plurality of (twelve in the present embodiment)teeth 12. Theteeth 12 are arranged in the circumferential direction and extend inward in the radial direction from theannular part 11. Thestator core 4 is formed by a stacking a plurality of core sheets in the axial direction. Each core sheet is formed by a metallic sheet having high permeability. Acoil 13 is wound around eachtooth 12 of thestator core 4 with an insulator (not shown) arranged in between. Thecoils 13 generate magnetic field, which rotates therotor 3. Eachcoil 13 is wound around a predetermined one of theteeth 12 and forms one of three-phases, namely, a U-phase, a V-phase, and a W-phase. Eachcoil 13 is wound in the same direction (counterclockwise when viewed theteeth 12 from the inner circumferential side) into a concentrated winding. Eachtooth 12 has a curveddistal surface 12 a, and thedistal surfaces 12 a of theteeth 12 lie along the same circle. - As shown in
FIGS. 1 and 2 , therotor 3 includes arotor core 22 having an annular shape. Arotary shaft 21 is fitted into therotor core 22. In the same manner as thestator core 4, therotor core 22 is formed by stackingcore sheets 22 a (refer toFIG. 3 ) in the axial direction. Eachcore sheet 22 a is a metallic sheet having high permeability. Fourmagnets 23 functioning as north poles are embedded in therotor core 22 near the outer circumferential surface of therotor core 22. Themagnets 23 are arranged at equal angular intervals (intervals of 90 degrees) in the circumferential direction. Eachmagnet 23 is formed by a generally rectangular plate. Therotor core 22 also includes twobridges 31 and aperipheral core portion 32 for eachmagnet 23. Thebridges 31 extend in the circumferential direction along opposite side surfaces of themagnet 23. Theperipheral core portion 32 is arranged outward in the radial direction from the magnet 23 (toward thestator 2 from the rotor core 22) and is supported by the twobridges 31. Theperipheral core portion 32 and themagnet 23 form amagnet pole 24. Thus, fourmagnet poles 24 are arranged at equal angular intervals of 90 degrees on the outer circumference of therotor core 22. -
Core poles 25, which project from therotor core 22, are arranged betweenadjacent magnet poles 24 with voids S1 and S2 formed at boundaries between themagnet poles 24 and thecore poles 25. The voids S1 and S2 are arranged at two opposite sides of eachmagnet pole 24 in the circumferential direction. The void S1 is located at the rear side of themagnet pole 24 relative to the rotation direction of the rotor 3 (clockwise inFIGS. 1 and 2 ). The void S2 is located at the front side of themagnet pole 24 relative to the rotation direction of therotor 3. Themagnets 23 and thecore poles 25 are arranged alternately at equal angular intervals (intervals of 45 degrees) in the circumferential direction. Therotor 3 includes eight magnet poles in total and has a consequent-pole structure in which themagnets 23 function as north poles and thecore poles 25 function as south poles. Eachcore pole 25 has acurved surface 25 a (surface facing the stator 2), and thecurved surfaces 25 a of thecore poles 25 lie along the same circle C as viewed from the axial direction. As shown inFIG. 2 , the circle C is a hypothetical circle extending along the outer circumference of therotor 3. - Each pair of
bridges 31 in therotor core 22 is in contact with the two circumferential side surfaces of thecorresponding magnet 23 and connects the correspondingperipheral core portion 32 to a central portion (main core portion 22 b) of therotor core 22. Theperipheral core portions 32 and themain core portion 22 b are in contact with the surfaces of the magnets 23 (the two opposite surfaces of themagnets 23 in the radial direction). In this manner, themagnets 23 are in contact with therotor core 22 on its four sides as viewed in the axial direction. Thus, themagnets 23 are rigidly held in therotor core 22. - As shown in
FIG. 3 , eachbridge 31 includes a plurality ofholes 33 arranged in the axial direction and extending in the circumferential direction. In detail, eachcore sheet 22 a of therotor core 22 includes arecess 22 c, which hollows in the axial direction. Theholes 33 in thebridge 31 are formed by therecesses 22 c of thecore sheets 22 a. - As shown in
FIGS. 1 and 2 , eachperipheral core portion 32 has a surface facing thedistal surface 12 a of theteeth 12. The surface facing thedistal surface 12 a of thetooth 12 is formed by a first opposingsurface 32 a and a second opposingsurface 32 b, which are arranged in the circumferential direction. In detail, the first opposingsurface 32 a extends from a first circumferential end of the peripheral core portion 32 (front end in the rotation direction) to a predetermined circumferential intermediate position P. The second opposingsurface 32 b extends from the circumferential intermediate position P of theperipheral core portion 32 to a second circumferential end (rear end in the rotation direction). In other words, the surface of theperipheral core portion 32 is formed by the first opposingsurface 32 a, which is located at the front side relative to the rotation direction of therotor 3, and the second opposingsurface 32 b, which is located at the rear side relative to the rotation direction of therotor 3. - The first opposing
surfaces 32 a are curved and lie along the same circle C as viewed in the axial direction. Thus, the first opposingsurfaces 32 a of theperipheral core portions 32 lie along the same circle C as thesurfaces 25 a of thecore poles 25. Further, the first opposingsurfaces 32 a are spaced apart from theteeth 12 in the radial direction by a distance that is constant in the circumferential direction. Each first opposingsurface 32 a has a circumferential width W1 that is equal to the circumferential width of thedistal surface 12 a of each tooth 12 (i.e., the surface facing therotor 3 in the radial direction). - The second opposing
surfaces 32 b are flat. The circumferential width of each second opposingsurface 32 b is less than the circumferential width W1 of each first opposingsurface 32 a. As viewed in the axial direction, the second opposingsurfaces 32 b are located inward in the radial direction from the circle C along which the first opposingsurfaces 32 a lie. In other words, the distance between each second opposingsurface 32 b and theteeth 12 is greater than the distance between each first opposingsurface 32 a and theteeth 12. The second opposingsurface 32 b is formed so that the distance from theteeth 12 in the radial direction gradually increases in the circumferential direction from the intermediate position P of the correspondingperipheral core portion 32 to the second circumferential end of theperipheral core portion 32. - As described above, the first opposing
surfaces 32 a of theperipheral core portions 32 are located on the circle C, whereas the second opposingsurfaces 32 b of theperipheral core portions 32 are located inward in the radial direction from the circle C. In this structure, each void S1, which is located at the rear side of thecorresponding magnet pole 24 relative to the rotation direction, extends to a region located outward in the radial direction from the magnet pole 24 (toward the stator 2). The extended region of the void S1 (hereafter referred to as the extended void region Sa) extends along the second opposingsurface 32 b to the circumferential intermediate position P of the correspondingperipheral core portion 32. In detail, the extended void region Sa extends from an outer radial end of the void S1 to the middle part of theperipheral core portion 32 in the circumferential direction (toward the middle point of the magnet pole). As a result, the extended void region Sa extends to a position located outward in the radial direction (toward the stator 2) from themagnet 23 arranged in themagnet pole 24. When viewed from the axial direction, the void S2, which is located at the front side in the rotational direction, has an area T2, and the void S2, which is located at the rear side in the rotational direction, has an area T1 (T1 is the area including the extended void region Sa) that is set to be equal to the area T2. That is, T2=T1 is set. - As shown in
FIG. 2 , eachmagnet 23, which has two parallel long sides and two parallel short sides, is arranged so that its long sides, as viewed in the axial direction, are inclined at a magnet inclination angle θ1 relative to a straight line L2 that is orthogonal to a straight line L1 extending in the radial direction of thestator core 4 through the middle point of the first opposingsurface 32 a of theperipheral core portion 32 in the circumferential direction. Themagnet 23 is inclined so that its rear end relative to the rotation direction is closer to the center of therotor 3, as viewed in the axial direction. The magnet width W2, which is the distance between the two ends of themagnet 23 in the circumferential direction, is greater than the width W1 of the first opposingsurface 32 a in the circumferential direction. Further, each second opposingsurface 32 b is inclined relative to a direction orthogonal to the long sides, or longitudinal direction, of the magnet 23 (the direction in which the short sides of themagnet 23 extends) at a void inclination angle θ2. - In the
brushless motor 1, thecoils 13 are supplied with a driving power to generate a rotational magnetic field that rotates therotor 3 in the clockwise direction. In this state, themagnet poles 24 generate torque that rotates therotor 3 mainly at the first opposingsurfaces 32 a of theperipheral core portions 32. When one first opposingsurface 32 a faces one tooth 12 (e.g.,tooth 12 b inFIG. 1 ), the adjacent tooth 12 (thetooth 12 c) faces the corresponding second opposingsurface 32 b. The gap between the second opposingsurface 32 b and thetooth 12 c is large due to the presence of the extended void region Sa. This reduces demagnetization in themagnet pole 24 caused by thetooth 12 c. As a result, the torque is increased, and the rotation performance is improved. Further, themagnet 23 is inclined so that the surface of theperipheral core portion 32 becomes farther as the rear end of themagnet 23 in the rotation direction becomes closer. This reduces the influence of thetooth 12 c on themagnet pole 24. -
FIG. 4 shows the change rate of the magnetic flux produced by themagnet pole 24 when the magnet inclination angle θ1 is varied in the range of 0 to 30 degrees.FIG. 4 shows four cases in which the void inclination angle θ2 is set at 30, 45, 60, and 75 degrees, respectively. InFIG. 4 , the magnet inclination angle θ1 that is set at 0 degree is used as a reference (in which the magnetic flux change rate is 1). When the void inclination angle θ2 is 30 degrees and 45 degrees and the magnet inclination angle θ1 is in the range of 0 to approximately 22.5 degrees, the magnetic flux change rate is greater than 1. This suggests that the magnetic flux density increases and is in a satisfactory range when the void inclination angle θ2 is set to 45 degrees or less and the magnet inclination angle θ1 is set in the range of 0°≦θ2≦22.5°. In the present embodiment, the void inclination angle θ2 and the magnet inclination angle θ1 are set in the above range to increase the magnetic flux density. - The above embodiment has the advantages described below.
- (1) In the present embodiment, the void S1 between each
magnet pole 24 and theadjacent core pole 25 includes the extended void region Sa, which extends into theperipheral core portion 32 toward the middle point of themagnet pole 24 in the circumferential direction. As a result, the extended void region Sa is arranged between theteeth 12 and part of eachmagnet pole 24 in the circumferential direction. When not only onetooth 12 faces themagnet pole 24 but theadjacent tooth 12 also faces thesame magnet pole 24 in the radial direction, the extended void region Sa reduces the influence of theadjacent tooth 12 on themagnet pole 24. This reduces demagnetization in themagnet pole 24 caused by theadjacent tooth 12. As a result, the torque is increased, and the rotation performance is improved. - (2) In the present embodiment, each
peripheral core portion 32 includes the first opposingsurface 32 a, which faces theteeth 12 and is spaced apart from the opposingtooth 12 by a first distance, and the second opposingsurface 32 b, which faces theteeth 12 and is spaced apart through the extended void region Sa from the correspondingteeth 12 by a second distance that is larger than the first distance. Thus, when one first opposingsurface 32 a faces not only thesingle tooth 12 but also theadjacent tooth 12, this ensures that demagnetization in themagnet pole 24 caused by theadjacent tooth 12 is reduced. - (3) In the present embodiment, the width W1 of the first opposing
surface 32 a in the circumferential direction is equal to the width of thedistal surface 12 a of eachtooth 12 in the circumferential direction. This efficiently generates torque with the first opposingsurfaces 32 a. As a result, even though the second opposingsurfaces 32 a reduce demagnetization, the decrease in torque is minimized. - (4) In the present embodiment, each
magnet 23 is formed by a rectangular plate. Themagnet 23 is arranged so that its long sides, as viewed in the axial direction of therotor 3, are inclined at the magnet inclination angle θ1 relative to the straight line L2 that is orthogonal to the straight line L1 extending in the radial direction of thestator core 4 through the middle point of the first opposingsurface 32 a in the circumferential direction. The second opposingsurface 32 b is flat and inclined at the void inclination angle θ2 relative to the direction in which the short sides of thecorresponding magnet 23 extend. The magnet inclination angle θ1 is set in the range of 0°≦θ1≦22.5°. The void inclination angle θ2 is set in the range of θ2≦45°. This increases the magnetic flux density (refer toFIG. 4 ) ensures further improvement in the rotation performance of therotor 3. - (5) In the present embodiment, each
bridge 31 includes theholes 33 arranged in the axial direction. Theholes 33 reduce passage of magnetic flux through thebridge 31 and prevent leakage of the magnetic field from thebridge 31. - (6) In the present embodiment, the
rotor core 22 thecore sheets 22 a that are stacked in the axial direction. Therecesses 22 c in thecore sheets 22 a form theholes 33 of eachbridge 31. Theholes 33 are easily formed in eachbridge 31 of therotor core 22 by forming therecess 22 c in eachcore sheet 22 a and then stacking thecore sheets 22 a. - (7) In the present embodiment, the
rotor 3 is rotatable in only one direction (clockwise direction as viewed inFIG. 1 ). Eachmagnet 23 is inclined so that portions closer to the front relative to the rotation direction are closer to the surface of the rotor 3 (i.e., the surface of the corresponding peripheral core portion 32). This increases the rotation torque. - It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.
- In the above embodiment, the
rotor 3 rotates in the clockwise direction. However, the rotation direction of therotor 3 may be changed to the counterclockwise direction without changing the structure of therotor 3. - In the above embodiment, the
bridges 31 are arranged on the two opposite ends of eachmagnet 23 in the circumferential direction. The voids S1 and S2 formed between themagnet poles 24 and thecore poles 25 function as grooves that open outward in the radial direction. However, the present invention is not limited in such a manner. Thebridges 31 may be modified to, for example, bridges 42 shown inFIGS. 5 and 6 . Thebridges 42 extend in the circumferential direction of therotor core 22 to connect theperipheral core portions 41 and thecore poles 25. Thebridges 42 extend in the circumferential direction from two opposite ends of eachperipheral core portion 41 and are connected to thesurfaces 25 a of theadjacent core poles 25. In the structure shown inFIGS. 5 and 6 , the surface of therotor 3 is formed by the outer circumferential surfaces of thebridges 42 in addition to thesurfaces 41 a and 25 a of theperipheral core portion 41 and thecore pole 25. The width W1 of the surface 41 a of each peripheral core portion 41 (i.e., the surface facing the teeth 12) in the circumferential direction is equal to the width of thedistal surface 12 a of eachtooth 12 in the circumferential direction. Therotor core 22 includesengagement projections 43, which prevent displacement of themagnets 23. Thebridges 42 are not in contact with the two opposite ends of the correspondingmagnets 23 in the circumferential direction. In this case, themagnets 23 are easily embedded in therotor core 22. In the structure shown inFIGS. 5 and 6 , thebridges 42 cover the outer side (portion closer to the stator 2) of the voids S1 and S2 between themagnet poles 24 and thecore poles 25. The extended void region Sa of each void S1 extends into the correspondingperipheral core portion 41. This structure also has the same advantages as the above embodiment. - In the above embodiment, each
peripheral core portion 32 includes a single first opposingsurface 32 a and a single second opposingsurface 32 b. However, the present invention is not limited to such a structure. As shown inFIG. 7 , for example, eachperipheral core portion 32 may include a first opposingsurface 32 a located in the middle of the surface of theperipheral core portion 32 in the circumferential direction and two second opposingsurfaces 32 b located at the two opposite sides of the first opposingsurface 32 a in the circumferential direction. In this structure, the voids S1 and S2 at the two circumferential ends of eachmagnet pole 24 each include an extended void region Sa. This structure may be used when therotor 3 is rotatable in both forward and rearward directions. When one first opposingsurface 32 a faces onetooth 12 and anadjacent tooth 12, this structure reduces demagnetization in themagnet pole 24 caused by theadjacent tooth 12 in a preferable manner regardless of whether therotor 3 rotates in the forward direction or the rearward direction. - In the structure shown in
FIG. 7 , the second opposingsurfaces 32 b are curved toward the center of therotor 3. In other words, the second opposingsurfaces 32 b are curved away from thestator 2 as viewed in the axial direction. In this structure, the distance between theperipheral core portion 32 and theteeth 12 suddenly changes at the two circumferential ends of theperipheral core portion 32. This reduces demagnetization at the second opposingsurfaces 32 b in a preferable manner. - In the structure shown in
FIG. 7 , themagnets 23 are arranged so that its longitudinal direction, as viewed in the axial direction, is orthogonal to a straight line L1 that extends in the radial direction of therotor core 22 through the circumferential middle point of themagnet pole 24. Eachmagnet pole 24 is symmetric relative to the straight line L1. -
FIG. 8 shows the change rate of the magnetic flux at themagnet poles 24 in the structure shown inFIG. 7 when the ratio W2/W1 is varied. The ratio W2/W1 is the ratio of the width W2 of themagnet 23 and the width W1 of the first opposingsurface 32 a in the circumferential direction.FIG. 8 shows five cases in which the ratio E/A is set at 0, 1, 2, 4, and 6, respectively. The ratio E/A is the ratio of the distance E from the two ends of theperipheral core portion 32 in the direction parallel to the short sides of the magnet 23 (the vertical direction inFIG. 7 ) to the circle C (edge depth E inFIG. 7 ) and the distance A (air void A) in the radial direction from the first opposingsurface 32 a (the circle C) to thedistal surface 12 a of thetooth 12.FIG. 9 is a referential diagram showing a structure in which the edge depth E is 0 is substantially equal to the magnet width W2 and the circumferential width W1 of the first opposingsurface 32 a (i.e., structure of ratio W2/W1≈1).FIG. 10 shows a structure in which the edge depth E is 0 and the ratio W2/W1=1.49. In the structure shown inFIG. 10 , the edge width E=0 is satisfied and anedge 44 at each of the two ends of eachperipheral core portion 32 lies along the circle C. However, the first opposingsurface 32 a, the second opposingsurfaces 32 b, and the extended void region Sa are formed in the surface of eachperipheral core portion 32. The structure shown inFIG. 10 thus has the same advantages as the structure shown inFIG. 7 , specifically, the extended void region Sa reduces demagnetization.FIG. 8 is a graph showing the characteristics when the width W1 of the first opposingsurface 32 a in the circumferential direction is set equal to thedistal surface 12 a of thetooth 12 and the volume of themagnet 23 is constant as shown inFIGS. 9 and 10 and the magnet width W2 is varied. - In
FIG. 8 , the edge depth ratio E/A that is set at 0 is used as a reference (in which the magnetic flux change ratio is 1). When the edge depth ratio E/A is set at 0 and the ratio W2/W1 in the range of 1.0<W2/W1<2.1, the magnetic flux density increased and is thus in a satisfactory range. The structure in which the edge depth ratio E/A is set at 0 and the ratio W2/W1 is set in the range of 1.0<W2/W1<2.1 reduces demagnetization, and increases the torque, and improves the rotation performance. The edge depth ratio E/A set at 4 or less and the ratio W2/W1 set in the range of 1.2<W2/W1<1.8 also increase the magnetic flux density in an optimum manner. The structure in which the edge depth ratio E/A is set at 4 or less and the ratio W2/W1 is set in the range of 1.2<W2/W1<1.8 reduces demagnetization, increases the torque, and improves the rotation performance. When the edge depth ratio E/A is 6, the magnetic flux change ratio is 1 or less regardless of the ratio W2/W1. - In the structure shown in
FIG. 7 , each of themagnet pole 24 and thecore pole 25 are arranged to be symmetric relative to a circumferential middle line but not particularly limited to such a structure. For example, themagnet pole 24 andcore pole 25 may be in an asymmetric arrangement such as that shown inFIG. 11 . In this case, the circumferentially middle part in the surface of theperipheral core portion 32 defines the first opposingsurface 32 a. Further, the opposite sides of the first opposingsurface 32 a defines the second opposingsurfaces magnet 23 of eachmagnet pole 24 is arranged in therotor core 22 so that the longitudinal direction of themagnet 23 as viewed in the axial direction of therotor 3 is inclined by a magnet inclination angle θ1 relative to a straight line L2, which is orthogonal to a straight line L1 extending in the radial direction of thestator core 4 through the middle point of the first opposingsurface 32 a of theperipheral core portion 32 in the circumferential direction. As a result, themagnet 23 is inclined so that the end located at the rear side relative to the rotational direction as viewed in the axial direction is closer to the center of therotor 3. At least one of the second opposingsurfaces peripheral core portion 32 in the circumferential direction and further improves the demagnetization resistance. - Further, in the structure shown in
FIG. 5 , the surface of theperipheral core portion 41 defining the extended void region Sa is flat but not particularly limited in such a manner. For example, as shown inFIG. 12 , the surface of theperipheral core portion 41 defining the extended void region Sa may be acurved surface 41 b, which hollows toward themagnet 24. Thecurved surface 41 b may be squeezed from the peripheral side for formation. This increases the density at the end of theperipheral core portion 41 that is closer to the void S1 and further improves the demagnetization resistance. - In the
rotor 3 of the above embodiment, the shapes of themagnets 23 and the shape of therotor core 22, which includes theperipheral core portions 32, thecore poles 25, and thebridges 31, may be changed. - In the above embodiment, the
rotor 3 includes eight magnet poles, namely, the fourmagnet poles 24 and the fourcore poles 25. However, the present invention is not limited in such a manner. Therotor 3 may include an (n+1) number (whereas n is a natural number) ofmagnet poles 24 and an (n+1) number ofcore poles 25, which total to 2(n+1) number of poles. Further, in the above embodiment, thestator 2 includes twelveteeth 12 and twelve slots. Thestator 2 may include 3(m+1) number (whereas m is a natural number) of slots. - The numerical ranges in the above embodiment may be changed as required.
- The
brushless motor 1 in the above embodiment is of an inner rotor type but may be of an outer rotor type. - The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.
Claims (16)
1. A brushless motor comprising:
a rotor including a rotor core, wherein the rotor core includes a plurality of magnet poles, which are arranged in a circumferential direction of the rotor core, and a plurality of core poles, each arranged between two adjacent ones of the magnet poles in the circumferential direction, a magnet is embedded in each of the magnet poles, and a void is formed at a boundary between each of the core poles and an adjacent one of the magnet poles in the circumferential direction; and
a stator including a plurality of teeth, which are arranged at equal angular intervals in the circumferential direction facing the rotor in a radial direction of the rotor, and a plurality of coils wound around the teeth respectively,
wherein each magnet pole includes a peripheral core portion located closer to the stator than the corresponding magnet in the radial direction of the rotor, and at least one of the two voids formed at opposite circumferential sides of each magnet pole includes an extended void region that extends into the corresponding peripheral core portion and toward a middle point of the magnet pole in the circumferential direction.
2. The brushless motor according to claim 1 , wherein
each peripheral core portion includes a first opposing surface, which faces the teeth and is spaced apart from the teeth by a first distance, and a second opposing surface, which faces the teeth with the extended void region arranged in between and is spaced apart from the teeth by a second distance that is greater than the first distance.
3. The brushless motor according to claim 2 , wherein
the first opposing surface has a circumferential width and each tooth include a distal surface having a circumferential width that is equal to the circumferential width of the first opposing surface.
4. The brushless motor according to claim 2 , wherein each magnet is formed by a rectangular plate and is embedded in the rotor core in a state in which a long side of the magnet, as viewed in an axial direction of the rotor, is inclined at a magnet inclination angle θ1 relative to a straight line that is orthogonal to a straight line extending in a radial direction of the rotor core through a circumferential middle point of the corresponding first opposing surface,
the second opposing surface is flat and inclines at a void inclination angle θ2 relative to a short side of the magnet,
the magnet inclination angle θ1 is set in a range of 0°≦θ1≦22.5°, and
the void inclination angle θ2 is set in a range of θ2≦45°.
5. The brushless motor according to claim 2 , wherein the second opposing surface is curved away from the stator as viewed in an axial direction of the rotor.
6. The brushless motor according to claim 5 , wherein
the rotor includes an (n+1) number (whereas n is a natural number) of the magnet poles and an (n+1) number of the core poles that total to 2(n+1) number of poles,
the stator includes 3(m+1) number (whereas m is a natural number) of slots,
each of the magnet poles includes the first opposing surface, which is located in a circumferentially middle part of the peripheral core portion, and the second opposing surface, which is located at each of two circumferential sides of the first opposing surface,
each of the magnet poles is formed to be symmetric relative to a straight line extending in a radial direction of the stator core through a circumferential middle point of the magnet pole,
when E represents a distance from two circumferential ends of each peripheral core portion to a hypothetical circle lying along a surface of the rotor and A represents a distance from the corresponding first opposing surface to a distal surface of each tooth in the radial direction, a ratio E/A is set to 0, and
when W1 represents a circumferential width of the first opposing surface in each peripheral core portion and W2 represents a circumferential width of each magnet, a ratio W2/W1 is set in a range of 1.0<W2/W1<2.1.
7. The brushless motor according to claim 6 , wherein
the rotor includes eight magnet poles, which are four of the magnet poles and four of the core poles, and
the stator includes twelve of the teeth and twelve slots.
8. The brushless motor according to claim 5 , wherein
the rotor includes an (n+1) number (whereas n is a natural number) of the magnet poles and an (n+1) number of the core poles that total to 2(n+1) number of poles,
the stator includes 3(m+1) number (whereas m is a natural number) of slots,
each of the magnet poles includes the first opposing surface, which is located in a circumferentially middle part of the peripheral core portion, and the second opposing surface, which is located at each of two circumferential sides of the first opposing surface,
each of the magnet poles is formed to be symmetric relative to a straight line extending in a radial direction of the stator core through a circumferential middle point of the magnet pole,
when E represents a distance from two circumferential ends of each peripheral core portion to a hypothetical circle lying along a surface of the rotor and A represents a distance from the corresponding first opposing surface to a distal surface of each tooth in the radial direction, a ratio E/A is set to 4 or less, and
when W1 represents a circumferential width of the first opposing surface in each peripheral core portion and W2 represents a circumferential width of each magnet, a ratio W2/W1 is set in a range of 1.2<W2/W1<1.8.
9. The brushless motor according to claim 8 , wherein
the rotor includes eight magnet poles, which are four of the magnet poles and four of the core poles, and
the stator includes twelve of the teeth and twelve slots.
10. The brushless motor according to claim 1 , wherein the rotor core includes two bridges that support each peripheral core portion and extend along two circumferential ends of each magnet.
11. The brushless motor according to claim 1 , wherein the rotor core includes a bridge connecting the peripheral core portion to an adjacent one of the core poles and extending along the circumferential direction of the rotor core, and
the bridge covers the void with a portion of the bridge located close to the stator.
12. The brushless motor according to claim 11 , wherein the peripheral core portion includes a surface opposing the teeth and having a circumferential width, and each tooth includes a distal surface having a circumferential width that is equal to the circumferential width of the opposing surface of the peripheral core portion.
13. The brushless motor according to claim 10 , wherein the bridge includes a plurality of holes arranged in an axial direction.
14. The brushless motor according to claim 13 , wherein
the rotor core includes core sheets stacked in the axial direction, and
each of the holes is formed by a recess formed in each core sheet.
15. The brushless motor according to claim 11 , wherein the bridge includes a plurality of holes arranged in an axial direction.
16. The brushless motor according to claim 15 , wherein
the rotor core includes core sheets stacked in the axial direction, and
each of the holes is formed by a recess formed in each core sheet.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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JP2010-234483 | 2010-10-19 | ||
JP2010234483 | 2010-10-19 | ||
JP2011-221224 | 2011-10-05 | ||
JP2011221224A JP5806073B2 (en) | 2010-10-19 | 2011-10-05 | Brushless motor |
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US20120091845A1 true US20120091845A1 (en) | 2012-04-19 |
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US13/274,082 Abandoned US20120091845A1 (en) | 2010-10-19 | 2011-10-14 | Brushless motor |
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US (1) | US20120091845A1 (en) |
JP (1) | JP5806073B2 (en) |
CN (1) | CN102545516A (en) |
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US20150171680A1 (en) * | 2012-06-14 | 2015-06-18 | Daikin Industries, Ltd. | Interior permanent magnet rotary electric machine |
JP2015186354A (en) * | 2014-03-24 | 2015-10-22 | アイチエレック株式会社 | permanent magnet motor |
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US20150171680A1 (en) * | 2012-06-14 | 2015-06-18 | Daikin Industries, Ltd. | Interior permanent magnet rotary electric machine |
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US20150318743A1 (en) * | 2012-09-24 | 2015-11-05 | Mitsubishi Electric Corporation | Permanent magnet-embedded electric motor |
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US20150303748A1 (en) * | 2013-01-03 | 2015-10-22 | Abb Technology Ag | Rotor for an electric machine and electric machine including the same |
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US10135308B2 (en) * | 2013-01-25 | 2018-11-20 | Magna Powertrain Ag & Co Kg | Electrical machine and method for producing an electrical sheet |
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US10199889B2 (en) * | 2013-06-20 | 2019-02-05 | Otis Elevator Company | Electric machine having rotor with slanted permanent magnets |
US20160126790A1 (en) * | 2013-06-20 | 2016-05-05 | Otis Elevator Company | Electric machine having rotor with slanted permanent magnets |
JP2015186353A (en) * | 2014-03-24 | 2015-10-22 | アイチエレック株式会社 | permanent magnet motor |
JP2015186354A (en) * | 2014-03-24 | 2015-10-22 | アイチエレック株式会社 | permanent magnet motor |
US20170353067A1 (en) * | 2015-03-18 | 2017-12-07 | Aisin Aw Co., Ltd. | Rotor for rotory electric machine and manufacturing method |
US10714995B2 (en) * | 2015-03-18 | 2020-07-14 | Aisin Aw Co., Ltd. | Rotor for rotary electric machine and manufacturing method |
US10644550B2 (en) | 2015-04-28 | 2020-05-05 | Denso Corporation | Rotor for rotating electric machine |
US10411535B2 (en) * | 2015-04-28 | 2019-09-10 | Denso Corporation | Rotor for rotating electric machine |
US10374474B2 (en) * | 2015-09-30 | 2019-08-06 | Mitsubishi Electric Corporation | Permanent magnet motor |
US10291088B2 (en) | 2016-02-19 | 2019-05-14 | Kabushiki Kaisha Toyota Jidoshokki | Permanent magnet type rotating electric machine |
US10305337B2 (en) | 2016-03-10 | 2019-05-28 | Kabushiki Kaisha Toyota Jidoshokki | Permanent magnet type rotating electric machine |
US20200119604A1 (en) * | 2017-06-15 | 2020-04-16 | Moteurs Leroy-Somer | Rotary electric machine |
US11735967B2 (en) * | 2017-06-15 | 2023-08-22 | Moteurs Leroy-Somer | Rotary electric machine with rotor having permanent magnets with concave faces between two flat portions |
CN107196434A (en) * | 2017-06-21 | 2017-09-22 | 珠海格力节能环保制冷技术研究中心有限公司 | Rotor assembly and magneto |
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US11183913B2 (en) | 2017-06-21 | 2021-11-23 | Gree Green Refrigeration Technology Center Co., Ltd. Of Zhuhai | Permanent magnet motor |
US11411449B2 (en) * | 2018-12-14 | 2022-08-09 | Tdk Corporation | Rotating electrical machine with rotor having arch shaped permanent magnets with perpendicular reference surface |
US11482899B2 (en) * | 2018-12-14 | 2022-10-25 | Tdk Corporation | Rotating electrical machine with rotor having arc shaped permanent magnets |
US20220247242A1 (en) * | 2019-06-26 | 2022-08-04 | Sony Group Corporation | Motor and motor control device |
Also Published As
Publication number | Publication date |
---|---|
CN102545516A (en) | 2012-07-04 |
DE102011116211A1 (en) | 2012-04-19 |
JP2012110214A (en) | 2012-06-07 |
JP5806073B2 (en) | 2015-11-10 |
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